Writing utensil and method of manufacturing the writing utensil

Abstract

A novel writing utensil in which an ink holder unit can be inserted into, and extracted from, a housing/main shaft. Helicoid screw threads are formed on the outer circumferential surface of a coupling portion of the ink holder unit or an inner circumferential surface of the main shaft. The main shaft or the outer circumferential surface of the ink holder unit without the screw threads is made of an elastic material for allowing the screw threads to bite thereinto. The coupling portion of the ink holder unit can be threaded into the main housing or pressed in a straight line thereinto. The ink holder unit can be extracted by relatively rotating the ink holder unit and main housing.

I claim: 
     
       1. A writing utensil comprising: an ink holder unit having a first annular surface; and   a main shaft having a second annular surface,   one of the first and second annular surfaces having helicoidal threads formed thereon,   the other of the first and second annular surfaces comprising an elastic material and having no threads pre-formed thereon,   the first and second annular surfaces residing one within the other with the ink holder unit and the main shaft in operative relationship,   the first and second annular surfaces being relatively dimensioned so that the ink holder unit and the main shaft can be placed into operative relationship by translational movement and so that the helicoidal threads bite into the other of the first and second annular surfaces with the ink holder unit and the main shaft in the operative relationship.   
     
     
       2. The writing utensil according to claim 1 wherein the writing utensil has a tip end and a tail end, the ink holder unit comprises a tip stopper, a writing tip and a receptacle for a supply of ink to be communicated to the writing tip and the main shaft has a hollow portion into which the ink receptacle extends with the ink holder unit and main shaft in the operative relationship. 
     
     
       3. The writing utensil according to claim 2 wherein the writing utensil is a ball pen. 
     
     
       4. The writing utensil according to claim 2 wherein the helical threads are on the tip stopper. 
     
     
       5. The writing utensil according to claim 1 wherein the elastic material of the one of the first and second annular surfaces is harder than the elastic material of the other of the first and second annular surfaces. 
     
     
       6. The writing utensil according to claim 1 wherein the elastic material of the one of the first and second annular surfaces comprises plastic. 
     
     
       7. The writing utensil according to claim 1 wherein the elastic material of the one of the first and second annular surfaces comprises at least one of polypropylene resin, polyethylene resin, and polyester resin. 
     
     
       8. A method of manufacturing a writing utensil, said method comprising the steps of: providing an ink holder unit comprising a tip stopper with a writing tip and a first annular surface;   providing a main shaft with a second annular surface,   there being helical threads on one of the first and second annular surfaces and no threads pre-formed on the other of the first and second annular surfaces; and   directing the ink holder unit and main shaft, one against the other by translatory movement into an operative relationship wherein the first and second annular surfaces reside one within the other with the helicoid threads against the other of the first and second annular surface.